Occlusion Reduction and Magnification for Multidimensional Data Presentations

ABSTRACT

A method in a computer system for generating a presentation of a region-of-interest in an original image for display on a display screen, the original image being a collection of polygons having polygons defined by three or more shared edges joined at vertex points, the method comprising: establishing a lens for the region-of-interest, the lens having a magnified focal region for the region-of-interest at least partially surrounded by a shoulder region across which the magnification decreases, the focal and shoulder regions having respective perimeters; subdividing polygons in the collection of polygons proximate to at least one of the perimeters, as projected with the polygons onto a base plane, by inserting one or more additional vertex points and additional edges into the polygons to be subdivided; and, applying the lens to the original image to produce the presentation by displacing the vertex points onto the lens and perspectively projecting the displacing onto a view plane in a direction aligned with a viewpoint for the region-of-interest.

CROSS-REFERENCE

This application is a continuation of, and claims priority to U.S.patent application Ser. No. 11/214,886, entitled “Occlusion Reductionand Magnification for Multidimensional Data Presentations,” filed onAug. 31, 2005, which in-turn claims priority to U.S. Provisional PatentApplication Ser. No. 60/606,906, entitled “Occlusion Reduction andMagnification Methods and Applications for Multidimensional DataPresentation,” filed on Sep. 3, 2004, both of which are herebyincorporated by reference in their entirety.

BACKGROUND

Multidimensional and three-dimensional (“3D”) presentations ofinformation present specific challenges not found in two-dimensional(“2D”) presentations. For example, in 3D presentations certain elementsmay be occluded by the presence of other elements in the presentation.Traditional approaches to dealing with occlusion avoidance in 3Dpresentations include techniques such as cutting planes, viewernavigation, filtering of information, and transparency. While thesemethods provide clearer visual access to elements of interest, theyremove much of the contextual information from a presentation.

In 2D presentations all information is restricted to a planeperpendicular to a view point. The addition of the third spatialvariable (or z component) in 3D presentations allows objects to beinterposed or positioned between the viewpoint and other objects in ascene, thus partially or completely hiding them from view. Thepreservation of spatial relationships and presentation of relationshipsto the occluding objects is important in constructing a physicallyplausible scene, or in other words, for maintaining the detail of thescene in the context in which it exists. For example, in volumetricrendering of 3D data it is often the case that the near-continuousnature of the data makes occlusion of interior features of the datainevitable. This phenomenon is important in supporting the perception ofthe scene as a 3D presentation, but a user may very well wish to examinethese hidden interior features and regions.

Solutions are available that provide visual access (i.e., clear lines ofsight) to previously occluded elements. Several of these solutions aredescribed by Cowperthwaite (Cowperthwaite, David J., OcclusionResolution Operators for Three-Dimensional Detail-In-Context (Burnaby,British Columbia: Simon Fraser University, 2000), which is incorporatedherein by reference. Cutting planes may be used to remove informationfrom a scene. Increasing transparency (or reducing the opacity) ofobjects allows more distant objects to be seen through those moreproximal to the viewer. Navigation of the viewer, whether egocentric(moving the viewer within the data space) or exocentric (moving orre-orientation of the data space) may lead to a configuration whereocclusion is resolved. Finally, information filtering may be used toreduce the density of data in a representation. These are all commonmethods of occlusion resolution and all operate by reducing the amount(or visibility) of contextual information in the final presentation.Similar methods such as panning zooming and filtering have also beentraditionally applied to dealing with large or congested displays ofinformation in 2D. Thus, the removal of information from a presentationhas been one approach to dealing with occlusion in large informationspaces.

Another approach has been the development of “detail-in-context”presentation algorithms. The field of detail-in-context viewing isconcerned with the generation of classes of information presentationswhere areas or items defined as focal regions or regions-of-interest arepresented with an increased level of detail, without the removal ofcontextual information from the original presentation. For example,regions of greatest interest may be displayed at an enlarged size,providing more visual detail, while the scale of the surrounding contextmay be adjusted to provide the space for the magnification of theregion-of-interest.

Thus, in 3D computer graphics and 3D information presentationsgenerally, occlusion of objects of interest by other objects in theviewer's line of sight is a common problem. U.S. Pat. No. 6,798,412,which is incorporated herein by reference, describes methods ofocclusion reduction based on displacements orthogonal to the line ofsight and based on a variety of distance metrics and shaping functions.What are now needed are additional methods and improvements to methodsfor occlusion reduction and magnification.

A need therefore exists for an improved method and system for reducingocclusion and providing magnification in multidimensional datapresentations. Accordingly, a solution that addresses, at least in part,the above and other shortcomings is desired.

SUMMARY

According to one aspect, there is provided a method in a computer systemfor generating a presentation of a region-of-interest in an originalimage for display on a display screen, the original image being acollection of polygons having polygons defined by three or more sharededges joined at vertex points, the method comprising: establishing alens for the region-of-interest, the lens having a magnified focalregion for the region-of-interest at least partially surrounded by ashoulder region across which the magnification decreases, the focal andshoulder regions having respective perimeters; subdividing polygons inthe collection of polygons proximate to at least one of the perimeters,as projected with the polygons onto a base plane, by inserting one ormore additional vertex points and additional edges into the polygons tobe subdivided; and, applying the lens to the original image to producethe presentation by displacing the vertex points onto the lens andperspectively projecting the displacing onto a view plane in a directionaligned with a viewpoint for the region-of-interest.

According to another aspect, there is provided a method in a computersystem for generating a presentation of an object-of-interest in anoriginal image for display on a display screen, the original image beinga collection of objects, the object-of-interest being one object in thecollection, the method comprising: establishing a viewpoint for theobject-of-interest; establishing a path through the original imagebetween the viewpoint and the object-of-interest; extruding points onthe object-of-interest along the path toward the viewpoint to define avolume for determining minimum displacements from the path for objectsintersected by the volume; and, displacing one or more of the objectsaway from the path according to a transformation function and theminimum displacements to locations within the original image wheresubstantially all of the objects displaced remain visible and do notocclude the object-of-interest when viewed from the viewpoint.

In accordance with further aspects there is provided an apparatus suchas a data processing system, a method for adapting this system, as wellas articles of manufacture such as a computer readable medium havingprogram instructions recorded thereon for practicing the method of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the embodiments will become apparentfrom the following detailed description, taken in combination with theappended drawings, in which:

FIG. 1 is a graphical representation illustrating the geometry forconstructing a three-dimensional perspective viewing frustum, relativeto an x, y, z coordinate system, in accordance with elastic presentationspace graphics technology;

FIG. 2 is a graphical representation illustrating the geometry of apresentation in accordance with elastic presentation space graphicstechnology;

FIG. 3 is a block diagram illustrating a data processing system adaptedto implement an embodiment of the invention;

FIG. 4 is a partial screen capture illustrating a GUI having lenscontrol elements for user interaction with detail-in-context datapresentations;

FIG. 5 is a diagram illustrating an original configuration of a 2Dcross-sectional view of a structure;

FIG. 5A is a diagram illustrating extrusion of points on the surface ofthe object-of-interest along a path toward a viewpoint.

FIG. 6 is a diagram illustrating direction vectors to points in thestructure of FIG. 5 lying on or near a sight-line;

FIG. 7 is a diagram illustrating a final configuration resulting fromthe application of an occlusion reducing transformation function to thestructure of FIG. 5;

FIG. 8 is a diagram illustrating a distortion function or lens;

FIG. 9 is a diagram illustrating an original image or representation inthe form of a mesh composed of polygons (e.g., triangles);

FIG. 10 is a detail view of a portion of the mesh of FIG. 9; and,

FIG. 11 is a flow chart illustrating operations of software moduleswithin the memory of a data processing system for generating apresentation of a region-of-interest in an original image for display ona display screen, the original image being a collection of polygonshaving polygons defined by three or more shared edges joined at vertexpoints, in accordance with an embodiment of the invention.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding. However, it is understood that thetechniques described herein may be practiced without these specificdetails. The term “data processing system” is used herein to refer toany machine for processing data, including the navigation systems,computer systems, and network arrangements described herein. Theembodiments may be implemented in any computer programming languageprovided that the operating system of the data processing systemprovides the facilities that may support the requirements of the presentinvention. Any limitations presented would be a result of a particulartype of operating system or computer programming language and would notbe a limitation of the present embodiments.

The “screen real estate problem” generally arises whenever large amountsof information are to be displayed on a display screen of limited size.Known tools to address this problem include panning and zooming. Whilethese tools are suitable for a large number of visual displayapplications, they become less effective where sections of the visualinformation are spatially related, such as in layered maps andthree-dimensional representations, for example. In this type ofinformation display, panning and zooming are not as effective as much ofthe context of the panned or zoomed display may be hidden.

A recent solution to this problem is the application of“detail-in-context” presentation techniques. Detail-in-context is themagnification of a particular region-of-interest (the “focal region” or“detail”) in a data presentation while preserving visibility of thesurrounding information (the “context”). This technique hasapplicability to the display of large surface area media (e.g. digitalmaps) on computer screens of variable size including graphicsworkstations, laptop computers, personal digital assistants (“PDAs”),and cell phones.

In the detail-in-context discourse, differentiation is often madebetween the terms “representation” and “presentation”. A representationis a formal system, or mapping, for specifying raw information or datathat is stored in a computer or data processing system. For example, adigital map of a city is a representation of raw data including streetnames and the relative geographic location of streets and utilities.Such a representation may be displayed visually on a computer screen orprinted on paper. On the other hand, a presentation is a spatialorganization of a given representation that is appropriate for the taskat hand. Thus, a presentation of a representation organizes such thingsas the point of view and the relative emphasis of different parts orregions of the representation. For example, a digital map of a city maybe presented with a region magnified to reveal street names.

In general, a detail-in-context presentation may be considered as adistorted view (or distortion) of a portion of the originalrepresentation or image where the distortion is the result of theapplication of a “lens” like distortion function to the originalrepresentation. A detailed review of various detail-in-contextpresentation techniques such as “Elastic Presentation Space” (“EPS”) (or“Pliable Display Technology” (“PDT”)) may be found in a publication byMarianne S. T. Carpendale, entitled “A Framework for ElasticPresentation Space” (Carpendale, Marianne S. T., A Framework for ElasticPresentation Space (Burnaby, British Columbia: Simon Fraser University,1999)), and incorporated herein by reference.

In general, detail-in-context data presentations are characterized bymagnification of areas of an image where detail is desired, incombination with compression of a restricted range of areas of theremaining information (i.e. the context), the result typically givingthe appearance of a lens having been applied to the display surface.Using the techniques described by Carpendale, points in a representationare displaced in three dimensions and a perspective projection is usedto display the points on a two-dimensional presentation display. Thus,when a lens is applied to a two-dimensional continuous surfacerepresentation, for example, the resulting presentation appears to bethree-dimensional. In other words, the lens transformation appears tohave stretched the continuous surface in a third dimension. In EPSgraphics technology, a two-dimensional visual representation is placedonto a surface; this surface is placed in three-dimensional space; thesurface, containing the representation, is viewed through perspectiveprojection; and the surface is manipulated to effect the reorganizationof image details. The presentation transformation is separated into twosteps: surface manipulation or distortion and perspective projection.

FIG. 1 is a graphical representation illustrating the geometry 100 forconstructing a three-dimensional (“3D”) perspective viewing frustum 220,relative to an x, y, z coordinate system, in accordance with elasticpresentation space (EPS) graphics technology. In EPS technology,detail-in-context views of two-dimensional (“2D”) visual representationsare created with sight-line aligned distortions of a 2D informationpresentation surface within a 3D perspective viewing frustum 220. InEPS, magnification of regions of interest and the accompanyingcompression of the contextual region to accommodate this change in scaleare produced by the movement of regions of the surface towards theviewpoint (“VP”) 240 located at the apex of the pyramidal shape 220containing the frustum. The process of projecting these transformedlayouts via a perspective projection results in a new 2D layout whichincludes the zoomed and compressed regions. The use of the thirddimension and perspective distortion to provide magnification in EPSprovides a meaningful metaphor for the process of distorting theinformation presentation surface. The 3D manipulation of the informationpresentation surface in such a system is an intermediate step in theprocess of creating a new 2D layout of the information.

FIG. 2 is a graphical representation illustrating the geometry 200 of apresentation in accordance with EPS graphics technology. EPS graphicstechnology employs viewer-aligned perspective projections to producedetail-in-context presentations in a reference view plane 201 which maybe viewed on a display. Undistorted 2D data points are located in abasal plane 210 of a 3D perspective viewing volume or frustum 220 whichis defined by extreme rays 221 and 222 and the basal plane 210. The VP240 is generally located above the centre point of the basal plane 210and reference view plane (“RVP”) 201. Points in the basal plane 210 aredisplaced upward onto a distorted surface 230 which is defined by ageneral 3D distortion function (i.e. a detail-in-context distortionbasis function). The direction of the perspective projectioncorresponding to the distorted surface 230 is indicated by the lineFPo-FP 231 drawn from a point FPo 232 in the basal plane 210 through thepoint FP 233 which corresponds to the focus or focal region or focalpoint of the distorted surface 230. Typically, the perspectiveprojection has a direction 231 that is viewer-aligned (i.e., the pointsFPo 232, FP 233, and VP 240 are collinear).

EPS is applicable to multidimensional data and is well suited toimplementation on a computer for dynamic detail-in-context display on anelectronic display surface such as a monitor. In the case of twodimensional data, EPS is typically characterized by magnification ofareas of an image where detail is desired 233, in combination withcompression of a restricted range of areas of the remaining information(i.e. the context) 234, the end result typically giving the appearanceof a lens 230 having been applied to the display surface. The areas ofthe lens 230 where compression occurs may be referred to as the“shoulder” 234 of the lens 230. The area of the representationtransformed by the lens may be referred to as the “lensed area”. Thelensed area thus includes the focal region and the shoulder. Toreiterate, the source image or representation to be viewed is located inthe basal plane 210. Magnification 233 and compression 234 are achievedthrough elevating elements of the source image relative to the basalplane 210, and then projecting the resultant distorted surface onto thereference view plane 201. EPS performs detail-in-context presentation ofn-dimensional data through the use of a procedure wherein the data ismapped into a region in an (n+1) dimensional space, manipulated throughperspective projections in the (n+1) dimensional space, and then finallytransformed back into n-dimensional space for presentation. EPS hasnumerous advantages over conventional zoom, pan, and scrolltechnologies, including the capability of preserving the visibility ofinformation outside 234 the local region of interest 233.

For example, and referring to FIGS. 1 and 2, in two dimensions, EPS canbe implemented through the projection of an image onto a reference plane201 in the following manner. The source image or representation islocated on a basal plane 210, and those regions of interest 233 of theimage for which magnification is desired are elevated so as to move themcloser to a reference plane situated between the reference viewpoint 240and the reference view plane 201. Magnification of the focal region 233closest to the RVP 201 varies inversely with distance from the RVP 201.As shown in FIGS. 1 and 2, compression of regions 234 outside the focalregion 233 is a function of both distance from the RVP 201, and thegradient of the function describing the vertical distance from the RVP201 with respect to horizontal distance from the focal region 233. Theresultant combination of magnification 233 and compression 234 of theimage as seen from the reference viewpoint 240 results in a lens-likeeffect similar to that of a magnifying glass applied to the image.Hence, the various functions used to vary the magnification andcompression of the source image via vertical displacement from the basalplane 210 are described as lenses, lens types, or lens functions. Lensfunctions that describe basic lens types with point and circular focalregions, as well as certain more complex lenses and advancedcapabilities such as folding, have previously been described byCarpendale.

FIG. 3 is a block diagram illustrating a data processing system 300adapted to implement an embodiment. The data processing system 300 issuitable for implementing EPS technology, for displayingdetail-in-context presentations of representations in conjunction with adetail-in-context graphical user interface (“GUI”) 400, as describedbelow, and for controlling detail-in-context lenses in detail-in-contextpresentations while reducing occlusion and improving magnification. Thedata processing system 300 includes an input device 310, a centralprocessing unit (“CPU”) 320, memory 330, and a display 340. The inputdevice 310 may include a keyboard, a mouse, a trackball, an eye trackingdevice, a position tracking device, or a similar device. The CPU 320 mayinclude dedicated coprocessors and memory devices. The memory 330 mayinclude RAM, ROM, databases, or disk devices. And, the display 340 mayinclude a computer screen, terminal device, or a hardcopy producingoutput device such as a printer or plotter. The data processing system300 has stored therein data representing sequences of instructions whichwhen executed cause the method described herein to be performed. Ofcourse, the data processing system 300 may contain additional softwareand hardware a description of which is not necessary for understanding.

Thus, the data processing system 300 includes computer executableprogrammed instructions for directing the system 300 to implement theembodiments. The programmed instructions may be embodied in one or moresoftware modules 331 resident in the memory 330 of the data processingsystem 300. Alternatively, the programmed instructions may be embodiedon a computer readable medium (such as a CD disk or floppy disk) whichmay be used for transporting the programmed instructions to the memory330 of the data processing system 300. Alternatively, the programmedinstructions may be embedded in a computer-readable, signal-bearingmedium that is uploaded to a network by a vendor or supplier of theprogrammed instructions, and this signal-bearing medium may bedownloaded through an interface to the data processing system 300 fromthe network by end users or potential buyers.

As mentioned, detail-in-context presentations of data using techniquessuch as pliable surfaces, as described by Carpendale, are useful inpresenting large amounts of information on limited-size displaysurfaces. Detail-in-context views allow magnification of a particularregion-of-interest (the “focal region”) 233 in a data presentation whilepreserving visibility of the surrounding information 210. In thefollowing, a GUI 400 is described having lens control elements that canbe implemented in software and applied to the editing of multi-layerimages and to the control of detail-in-context data presentations. Thesoftware can be loaded into and run by the data processing system 300 ofFIG. 3. In general, applications in computer graphics systems arelaunched by the computer graphics system's operating system uponselection by a user from a menu or other GUI. A GUI is used to conveyinformation to and receive commands from users and generally includes avariety of GUI objects or controls, including icons, toolbars, drop-downmenus, text, dialog boxes, buttons, and the like. A user typicallyinteracts with a GUI by using a pointing device (e.g., a mouse) toposition a pointer or cursor over an object and “clicking” on theobject.

FIG. 4 is a partial screen capture illustrating a GUI 400 having lenscontrol elements for user interaction with detail-in-context datapresentations. Detail-in-context data presentations are characterized bymagnification of areas of an image where detail is desired, incombination with compression of a restricted range of areas of theremaining information (i.e. the context), the end result typicallygiving the appearance of a lens having been applied to the displayscreen surface. This lens 410 includes a “focal region” 420 having highmagnification, a surrounding “shoulder region” 430 where information istypically visibly compressed, and a “base” 412 surrounding the shoulderregion 430 and defining the extent of the lens 410. In FIG. 4, the lens410 is shown with a circular shaped base 412 (or outline) and with afocal region 420 lying near the center of the lens 410. However, thelens 410 and focal region 420 may have any desired shape. As mentionedabove, the base of the lens 412 may be coextensive with the focal region420.

In general, the GUI 400 has lens control elements that, in combination,provide for the interactive control of the lens 410. The effectivecontrol of the characteristics of the lens 410 by a user (i.e., dynamicinteraction with a detail-in-context lens) is advantageous. At any giventime, one or more of these lens control elements may be made visible tothe user on the display surface 340 by appearing as overlay icons on thelens 410. Interaction with each element is performed via the motion ofan input or pointing device 310 (e.g., a mouse) with the motionresulting in an appropriate change in the corresponding lenscharacteristic. As will be described, selection of which lens controlelement is actively controlled by the motion of the pointing device 310at any given time is determined by the proximity of the iconrepresenting the pointing device 310 (e.g. cursor) on the displaysurface 340 to the appropriate component of the lens 410. For example,“dragging” of the pointing device at the periphery of the boundingrectangle of the lens base 412 causes a corresponding change in the sizeof the lens 410 (i.e. “resizing”). Thus, the GUI 400 provides the userwith a visual representation of which lens control element is beingadjusted through the display of one or more corresponding icons.

For ease of understanding, the following discussion will be in thecontext of using a two-dimensional pointing device 310 that is a mouse,but it will be understood that the embodiments may be practiced withother 2D or 3D (or even greater numbers of dimensions) pointing devicesincluding a trackball, a keyboard, an eye tracking device, and aposition tracking device.

A mouse 310 controls the position of a cursor icon 401 that is displayedon the display screen 340. The cursor 401 is moved by moving the mouse310 over a flat surface, such as the top of a desk, in the desireddirection of movement of the cursor 401. Thus, the two-dimensionalmovement of the mouse 310 on the flat surface translates into acorresponding two-dimensional movement of the cursor 401 on the displayscreen 340.

A mouse 310 typically has one or more finger actuated control buttons(i.e. mouse buttons). While the mouse buttons can be used for differentfunctions such as selecting a menu option pointed at by the cursor 401,the disclosed embodiment may use a single mouse button to “select” alens 410 and to trace the movement of the cursor 401 along a desiredpath. Specifically, to select a lens 410, the cursor 401 is firstlocated within the extent of the lens 410. In other words, the cursor401 is “pointed” at the lens 410. Next, the mouse button is depressedand released. That is, the mouse button is “clicked”. Selection is thusa point and click operation. To trace the movement of the cursor 401,the cursor 401 is located at the desired starting location, the mousebutton is depressed to signal the computer 320 to activate a lenscontrol element, and the mouse 310 is moved while maintaining the buttondepressed. After the desired path has been traced, the mouse button isreleased. This procedure is often referred to as “clicking” and“dragging” (i.e. a click and drag operation). It will be understood thata predetermined key on a keyboard 310 could also be used to activate amouse click or drag. In the following, the term “clicking” will refer tothe depression of a mouse button indicating a selection by the user andthe term “dragging” will refer to the subsequent motion of the mouse 310and cursor 401 without the release of the mouse button.

The GUI 400 may include the following lens control elements: move,pickup, resize base, resize focus, fold, magnify, zoom, and scoop. Eachof these lens control elements has at least one lens control icon oralternate cursor icon associated with it. In general, when a lens 410 isselected by a user through a point and click operation, the followinglens control icons may be displayed over the lens 410: pickup icon 450,base outline icon 412, base bounding rectangle icon 411, focal regionbounding rectangle icon 421, handle icons 481, 482, 491 magnify slidebar icon 440, zoom icon 495, and scoop slide bar icon (not shown).Typically, these icons are displayed simultaneously after selection ofthe lens 410. In addition, when the cursor 401 is located within theextent of a selected lens 410, an alternate cursor icon 460, 470, 480,490, 495 may be displayed over the lens 410 to replace the cursor 401 ormay be displayed in combination with the cursor 401. These lens controlelements, corresponding icons, and their effects on the characteristicsof a lens 410 are described below with reference to FIG. 4.

In general, when a lens 410 is selected by a point and click operation,bounding rectangle icons 411, 421 are displayed surrounding the base 412and focal region 420 of the selected lens 410 to indicate that the lens410 has been selected. With respect to the bounding rectangles 411, 421one might view them as glass windows enclosing the lens base 412 andfocal region 420, respectively. The bounding rectangles 411, 421 includehandle icons 481, 482, 491 allowing for direct manipulation of theenclosed base 412 and focal region 420 as will be explained below. Thus,the bounding rectangles 411, 421 not only inform the user that the lens410 has been selected, but also provide the user with indications as towhat manipulation operations might be possible for the selected lens 410though use of the displayed handles 481, 482, 491. Note that it is wellwithin the scope of the present embodiment to provide a bounding regionhaving a shape other than generally rectangular. Such a bounding regioncould be of any of a great number of shapes including oblong, oval,ovoid, conical, cubic, cylindrical, polyhedral, spherical, etc.

Moreover, the cursor 401 provides a visual cue indicating the nature ofan available lens control element. As such, the cursor 401 willgenerally change in form by simply pointing to a different lens controlicon 450, 412, 411, 421, 481, 482, 491, 440. For example, when resizingthe base 412 of a lens 410 using a corner handle 491, the cursor 401will change form to a resize icon 490 once it is pointed at (i.e.positioned over) the corner handle 491. The cursor 401 will remain inthe form of the resize icon 490 until the cursor 401 has been moved awayfrom the corner handle 491.

Lateral movement of a lens 410 is provided by the move lens controlelement of the GUI 400. This functionality is accomplished by the userfirst selecting the lens 410 through a point and click operation. Then,the user points to a point within the lens 410 that is other than apoint lying on a lens control icon 450, 412, 411, 421, 481, 482, 491,440. When the cursor 401 is so located, a move icon 460 is displayedover the lens 410 to replace the cursor 401 or may be displayed incombination with the cursor 401. The move icon 460 not only informs theuser that the lens 410 may be moved, but also provides the user withindications as to what movement operations are possible for the selectedlens 410. For example, the move icon 460 may include arrowheadsindicating up, down, left, and right motion. Next, the lens 410 is movedby a click and drag operation in which the user clicks and drags thelens 410 to the desired position on the screen 340 and then releases themouse button 310. The lens 410 is locked in its new position until afurther pickup and move operation is performed.

Lateral movement of a lens 410 is also provided by the pickup lenscontrol element of the GUI. This functionality is accomplished by theuser first selecting the lens 410 through a point and click operation.As mentioned above, when the lens 410 is selected a pickup icon 450 isdisplayed over the lens 410 near the centre of the lens 410. Typically,the pickup icon 450 will be a crosshairs. In addition, a base outline412 is displayed over the lens 410 representing the base 412 of the lens410. The crosshairs 450 and lens outline 412 not only inform the userthat the lens has been selected, but also provides the user with anindication as to the pickup operation that is possible for the selectedlens 410. Next, the user points at the crosshairs 450 with the cursor401. Then, the lens outline 412 is moved by a click and drag operationin which the user clicks and drags the crosshairs 450 to the desiredposition on the screen 340 and then releases the mouse button 310. Thefull lens 410 is then moved to the new position and is locked thereuntil a further pickup operation is performed. In contrast to the moveoperation described above, with the pickup operation, it is the outline412 of the lens 410 that the user repositions rather than the full lens410.

Resizing of the base 412 (or outline) of a lens 410 is provided by theresize base lens control element of the GUI. After the lens 410 isselected, a bounding rectangle icon 411 is displayed surrounding thebase 412. For a rectangular shaped base 412, the bounding rectangle icon411 may be coextensive with the perimeter of the base 412. The boundingrectangle 411 includes handles 491. These handles 491 can be used tostretch the base 412 taller or shorter, wider or narrower, orproportionally larger or smaller. The corner handles 491 will keep theproportions the same while changing the size. The middle handles (notshown) will make the base 412 taller or shorter, wider or narrower.Resizing the base 412 by the corner handles 491 will keep the base 412in proportion. Resizing the base 412 by the middle handles will changethe proportions of the base 412. That is, the middle handles change theaspect ratio of the base 412 (i.e. the ratio between the height and thewidth of the bounding rectangle 411 of the base 412). When a user pointsat a handle 491 with the cursor 401 a resize icon 490 may be displayedover the handle 491 to replace the cursor 401 or may be displayed incombination with the cursor 401. The resize icon 490 not only informsthe user that the handle 491 may be selected, but also provides the userwith indications as to the resizing operations that are possible withthe selected handle. For example, the resize icon 490 for a cornerhandle 491 may include arrows indicating proportional resizing. Theresize icon (not shown) for a middle handle may include arrowsindicating width resizing or height resizing. After pointing at thedesired handle 491 the user would click and drag the handle 491 untilthe desired shape and size for the base 412 is reached. Once the desiredshape and size are reached, the user would release the mouse button 310.The base 412 of the lens 410 is then locked in its new size and shapeuntil a further base resize operation is performed.

Resizing of the focal region 420 of a lens 410 is provided by the resizefocus lens control element of the GUI. After the lens 410 is selected, abounding rectangle icon 421 is displayed surrounding the focal region420. For a rectangular shaped focal region 420, the bounding rectangleicon 421 may be coextensive with the perimeter of the focal region 420.The bounding rectangle 421 includes handles 481, 482. These handles 481,482 can be used to stretch the focal region 420 taller or shorter, wideror narrower, or proportionally larger or smaller. The corner handles 481will keep the proportions the same while changing the size. The middlehandles 482 will make the focal region 420 taller or shorter, wider ornarrower. Resizing the focal region 420 by the corner handles 481 willkeep the focal region 420 in proportion. Resizing the focal region 420by the middle handles 482 will change the proportions of the focalregion 420. That is, the middle handles 482 change the aspect ratio ofthe focal region 420 (i.e. the ratio between the height and the width ofthe bounding rectangle 421 of the focal region 420). When a user pointsat a handle 481, 482 with the cursor 401 a resize icon 480 may bedisplayed over the handle 481, 482 to replace the cursor 401 or may bedisplayed in combination with the cursor 401. The resize icon 480 notonly informs the user that a handle 481, 482 may be selected, but alsoprovides the user with indications as to the resizing operations thatare possible with the selected handle. For example, the resize icon 480for a corner handle 481 may include arrows indicating proportionalresizing. The resize icon 480 for a middle handle 482 may include arrowsindicating width resizing or height resizing. After pointing at thedesired handle 481, 482, the user would click and drag the handle 481,482 until the desired shape and size for the focal region 420 isreached. Once the desired shape and size are reached, the user wouldrelease the mouse button 310. The focal region 420 is then locked in itsnew size and shape until a further focus resize operation is performed.

Folding of the focal region 420 of a lens 410 is provided by the foldcontrol element of the GUI. In general, control of the degree anddirection of folding (i.e. skewing of the viewer aligned vector 231 asdescribed by Carpendale) is accomplished by a click and drag operationon a point 471, other than a handle 481, 482, on the bounding rectangle421 surrounding the focal region 420. The direction of folding isdetermined by the direction in which the point 471 is dragged. Thedegree of folding is determined by the magnitude of the translation ofthe cursor 401 during the drag. In general, the direction and degree offolding corresponds to the relative displacement of the focus 420 withrespect to the lens base 410. In other words, and referring to FIG. 2,the direction and degree of folding corresponds to the displacement ofthe point FP 233 relative to the point FPo 232, where the vector joiningthe points FPo 232 and FP 233 defines the viewer aligned vector 231. Inparticular, after the lens 410 is selected, a bounding rectangle icon421 is displayed surrounding the focal region 420. The boundingrectangle 421 includes handles 481, 482. When a user points at a point471, other than a handle 481, 482, on the bounding rectangle 421surrounding the focal region 420 with the cursor 401, a fold icon 470may be displayed over the point 471 to replace the cursor 401 or may bedisplayed in combination with the cursor 401. The fold icon 470 not onlyinforms the user that a point 471 on the bounding rectangle 421 may beselected, but also provides the user with indications as to what foldoperations are possible. For example, the fold icon 470 may includearrowheads indicating up, down, left, and right motion. By choosing apoint 471, other than a handle 481, 482, on the bounding rectangle 421 auser may control the degree and direction of folding. To control thedirection of folding, the user would click on the point 471 and drag inthe desired direction of folding. To control the degree of folding, theuser would drag to a greater or lesser degree in the desired directionof folding. Once the desired direction and degree of folding is reached,the user would release the mouse button 310. The lens 410 is then lockedwith the selected fold until a further fold operation is performed.

Magnification of the lens 410 is provided by the magnify lens controlelement of the GUI. After the lens 410 is selected, the magnify controlis presented to the user as a slide bar icon 440 near or adjacent to thelens 410 and typically to one side of the lens 410. Sliding the bar 441of the slide bar 440 results in a proportional change in themagnification of the lens 410. The slide bar 440 not only informs theuser that magnification of the lens 410 may be selected, but alsoprovides the user with an indication as to what level of magnificationis possible. The slide bar 440 includes a bar 441 that may be slid upand down, or left and right, to adjust and indicate the level ofmagnification. To control the level of magnification, the user wouldclick on the bar 441 of the slide bar 440 and drag in the direction ofdesired magnification level. Once the desired level of magnification isreached, the user would release the mouse button 310. The lens 410 isthen locked with the selected magnification until a furthermagnification operation is performed. In general, the focal region 420is an area of the lens 410 having constant magnification (i.e. if thefocal region is a plane). Again referring to FIGS. 1 and 2,magnification of the focal region 420, 233 varies inversely with thedistance from the focal region 420, 233 to the reference view plane(RVP) 201. Magnification of areas lying in the shoulder region 430 ofthe lens 410 also varies inversely with their distance from the RVP 201.Thus, magnification of areas lying in the shoulder region 430 will rangefrom unity at the base 412 to the level of magnification of the focalregion 420.

Zoom functionality is provided by the zoom lens control element of theGUI. Referring to FIG. 2, the zoom lens control element, for example,allows a user to quickly navigate to a region of interest 233 within acontinuous view of a larger presentation 210 and then zoom in to thatregion of interest 233 for detailed viewing or editing. Referring toFIG. 4, the combined presentation area covered by the focal region 420and shoulder region 430 and surrounded by the base 412 may be referredto as the “extent of the lens”. Similarly, the presentation area coveredby the focal region 420 may be referred to as the “extent of the focalregion”. The extent of the lens may be indicated to a user by a basebounding rectangle 411 when the lens 410 is selected. The extent of thelens may also be indicated by an arbitrarily shaped figure that boundsor is coincident with the perimeter of the base 412. Similarly, theextent of the focal region may be indicated by a second boundingrectangle 421 or arbitrarily shaped figure. The zoom lens controlelement allows a user to: (a) “zoom in” to the extent of the focalregion such that the extent of the focal region fills the display screen340 (i.e. “zoom to focal region extent”); (b) “zoom in” to the extent ofthe lens such that the extent of the lens fills the display screen 340(i.e. “zoom to lens extent”); or, (c) “zoom in” to the area lyingoutside of the extent of the focal region such that the area without thefocal region is magnified to the same level as the extent of the focalregion (i.e. “zoom to scale”).

In particular, after the lens 410 is selected, a bounding rectangle icon411 is displayed surrounding the base 412 and a bounding rectangle icon421 is displayed surrounding the focal region 420. Zoom functionality isaccomplished by the user first selecting the zoom icon 495 through apoint and click operation When a user selects zoom functionality, a zoomcursor icon 496 may be displayed to replace the cursor 401 or may bedisplayed in combination with the cursor 401. The zoom cursor icon 496provides the user with indications as to what zoom operations arepossible. For example, the zoom cursor icon 496 may include a magnifyingglass. By choosing a point within the extent of the focal region, withinthe extent of the lens, or without the extent of the lens, the user maycontrol the zoom function. To zoom in to the extent of the focal regionsuch that the extent of the focal region fills the display screen 340(i.e. “zoom to focal region extent”), the user would point and clickwithin the extent of the focal region. To zoom in to the extent of thelens such that the extent of the lens fills the display screen 340 (i.e.“zoom to lens extent”), the user would point and click within the extentof the lens. Or, to zoom in to the presentation area without the extentof the focal region, such that the area without the extent of the focalregion is magnified to the same level as the extent of the focal region(i.e. “zoom to scale”), the user would point and click without theextent of the lens. After the point and click operation is complete, thepresentation is locked with the selected zoom until a further zoomoperation is performed.

Alternatively, rather than choosing a point within the extent of thefocal region, within the extent of the lens, or without the extent ofthe lens to select the zoom function, a zoom function menu with multipleitems (not shown) or multiple zoom function icons (not shown) may beused for zoom function selection. The zoom function menu may bepresented as a pull-down menu. The zoom function icons may be presentedin a toolbar or adjacent to the lens 410 when the lens is selected.Individual zoom function menu items or zoom function icons may beprovided for each of the “zoom to focal region extent”, “zoom to lensextent”, and “zoom to scale” functions described above. In thisalternative, after the lens 410 is selected, a bounding rectangle icon411 may be displayed surrounding the base 412 and a bounding rectangleicon 421 may be displayed surrounding the focal region 420. Zoomfunctionality is accomplished by the user selecting a zoom function fromthe zoom function menu or via the zoom function icons using a point andclick operation. In this way, a zoom function may be selected withoutconsidering the position of the cursor 401 within the lens 410.

The concavity or “scoop” of the shoulder region 430 of the lens 410 isprovided by the scoop lens control element of the GUI. After the lens410 is selected, the scoop control is presented to the user as a slidebar icon (not shown) near or adjacent to the lens 410 and typicallybelow the lens 410. Sliding the bar (not shown) of the slide bar resultsin a proportional change in the concavity or scoop of the shoulderregion 430 of the lens 410. The slide bar not only informs the user thatthe shape of the shoulder region 430 of the lens 410 may be selected,but also provides the user with an indication as to what degree ofshaping is possible. The slide bar includes a bar (not shown) that maybe slid left and right, or up and down, to adjust and indicate thedegree of scooping. To control the degree of scooping, the user wouldclick on the bar of the slide bar and drag in the direction of desiredscooping degree. Once the desired degree of scooping is reached, theuser would release the mouse button 310. The lens 410 is then lockedwith the selected scoop until a further scooping operation is performed.

Advantageously, a user may choose to hide one or more lens control icons450, 412, 411, 421, 481, 482, 491, 440, 495 shown in FIG. 4 from view soas not to impede the user's view of the image within the lens 410. Thismay be helpful, for example, during an editing or move operation. A usermay select this option through means such as a menu, toolbar, or lensproperty dialog box.

In addition, the GUI 400 maintains a record of control elementoperations such that the user may restore pre-operation presentations.This record of operations may be accessed by or presented to the userthrough “Undo” and “Redo” icons 497, 498, through a pull-down operationhistory menu (not shown), or through a toolbar.

Thus, detail-in-context data viewing techniques allow a user to viewmultiple levels of detail or resolution on one display 340. Theappearance of the data display or presentation is that of one or morevirtual lenses showing detail 233 within the context of a larger areaview 210. Using multiple lenses in detail-in-context data presentationsmay be used to compare two regions of interest at the same time. Foldingenhances this comparison by allowing the user to pull the regions ofinterest closer together. Moreover, using detail-in-context technologysuch as PDT, an area of interest can be magnified to pixel levelresolution, or to any level of detail available from the sourceinformation, for in-depth review. The digital images may include graphicimages, maps, photographic images, or text documents, and the sourceinformation may be in raster, vector, or text form.

For example, in order to view a selected object or area in detail, auser can define a lens 410 over the object using the GUI 400. The lens410 may be introduced to the original image to form the a presentationthrough the use of a pull-down menu selection, tool bar icon, etc. Usinglens control elements for the GUI 400, such as move, pickup, resizebase, resize focus, fold, magnify, zoom, and scoop, as described above,the user adjusts the lens 410 for detailed viewing of the object orarea. Using the magnify lens control element, for example, the user maymagnify the focal region 420 of the lens 410 to pixel quality resolutionrevealing detailed information pertaining to the selected object orarea. That is, a base image (i.e., the image outside the extent of thelens) is displayed at a low resolution while a lens image (i.e., theimage within the extent of the lens) is displayed at a resolution basedon a user selected magnification 440, 441.

In operation, the data processing system 300 employs EPS techniques withan input device 310 and GUI 400 for selecting objects or areas fordetailed display to a user on a display screen 340. Data representing anoriginal image or representation is received by the CPU 320 of the dataprocessing system 300. Using EPS techniques, the CPU 320 processes thedata in accordance with instructions received from the user via an inputdevice 310 and GUI 400 to produce a detail-in-context presentation. Thepresentation is presented to the user on a display screen 340. It willbe understood that the CPU 320 may apply a transformation to theshoulder region 430 surrounding the region-of-interest 420 to affectblending or folding in accordance with EPS technology. For example, thetransformation may map the region-of-interest 420 and/or shoulder region430 to a predefined lens surface, defined by a transformation ordistortion function and having a variety of shapes, using EPStechniques. Or, the lens 410 may be simply coextensive with theregion-of-interest 420.

The lens control elements of the GUI 400 are adjusted by the user via aninput device 310 to control the characteristics of the lens 410 in thedetail-in-context presentation. Using an input device 310 such as amouse, a user adjusts parameters of the lens 410 using icons and scrollbars of the GUI 400 that are displayed over the lens 410 on the displayscreen 340. The user may also adjust parameters of the image of the fullscene. Signals representing input device 310 movements and selectionsare transmitted to the CPU 320 of the data processing system 300 wherethey are translated into instructions for lens control.

Moreover, the lens 410 may be added to the presentation before or afterthe object or area is selected. That is, the user may first add a lens410 to a presentation or the user may move a pre-existing lens intoplace over the selected object or area. The lens 410 may be introducedto the original image to form the presentation through the use of apull-down menu selection, tool bar icon, etc.

Advantageously, by using a detail-in-context lens 410 to select anobject or area for detailed information gathering, a user can view alarge area (i.e., outside the extent of the lens 410) while focusing inon a smaller area (or within the focal region 420 of the lens 410)surrounding the selected object. This makes it possible for a user toaccurately gather detailed information without losing visibility orcontext of the portion of the original image surrounding the selectedobject.

Now, according to the present embodiment, improved methods are providedfor occlusion reduction and magnification for multidimensional datapresentations.

In 3D computer graphics and 3D information presentations generally,occlusion of objects of interest by other objects in the viewer's lineof sight is a common problem. U.S. Pat. No. 6,798,412, which isincorporated herein by reference, describes methods of occlusionreduction based on displacements orthogonal to the line of sight andbased on a variety of distance metrics and shaping functions. Thepresent embodiment provides additional methods and improvements tomethods for occlusion reduction. Furthermore, a lens definition thatcombines occlusion reduction and magnification is provided.

For reference, FIGS. 5-7 show 2D cross-sectional views of a linearocclusion reducing transformation in operation. FIG. 5 is a diagramillustrating an original configuration 500 of the 2D cross-sectionalview of a structure 510. The structure 510 is defined by a number ofinformation points 501 arranged in a matrix. A region-of-interest (or anobject-of-interest) 520 is shown near the centre of the structure 510. Aviewpoint 530 for the region-of-interest 520 is shown near the bottomright-hand side of the structure 510. A sight-line 540 connects theregion-of-interest 520 to the viewpoint 530. In other words, theregion-of-interest 520 and the viewpoint 530 define the line of sightthrough the structure 510.

FIG. 5A is a diagram illustrating extrusion of points on theobject-of-interest (illustrated as lines 502, 504 extending from theobject-of-interest 520) along the path, such as the sight-line 540,toward the viewpoint 530. The extrusions, represented as lines 502, 504,form a volume that may be used to determine minimum displacements fromthe path for objects intersected by the volume. By extruding the pointson the object-of-interest 520, objects that occlude theobject-of-interest may be displaced away from the path. For example, thepoints 501 intersected by the lines 502, 504 or lying within the volumeformed by lines 502, 504 may be displaced away from the sight-line 540according to a transformation function and the minimum displacements tolocations within the original image, such as shown in FIG. 6.

FIG. 6 is a diagram illustrating direction vectors 650 to points 670 inthe structure 510 of FIG. 5 lying on or near the sight-line 540. Thedistance of each point 670 is measured to the nearest point 660 on thesight-line 540. A direction vector 650 from the nearest point 660 on thesight-line 540 to the point being adjusted 670 is also determined. Whenthe occlusion reducing transformation is applied, points will be movedin the direction of these direction vectors 650. The lengths of thedirection vectors 650 form an input to a transformation function. Theresult of this function is used to determine the displacement for eachpoint. Points closest to the line of sight are moved the furthest indistance, and points originally lying further away are moved insuccessively smaller increments in distance. In other words, the lengthsof the direction vectors 650 form inputs to the function that determinesthe magnitude of resulting displacement vectors. The direction of theresulting displacement vectors will be parallel to the input directionvectors. Eventually a smooth transition is made to points which are farenough away as to be unaffected by the transformation.

FIG. 7 is a diagram illustrating a final configuration 700 resultingfrom the application of the occlusion reducing transformation functionto the structure 510 of FIG. 5. In this final configuration 700, a clearline of sight from the viewpoint 530 to the region-of-interest 520 isestablished. Thus, the effect of an occlusion reducing transformation isto provide a clear line of sight, or visual access, to an object orregion-of-interest within a 3D visual representation by adjusting thelayout.

It is helpful to know the magnitude of the displacements required toclear the line of sight 540 to the object of interest 520 for themethods described in U.S. Pat. No. 6,798,412. According to oneembodiment, the amplitude of displacements is increased until anextrusion of the object of interest 520 toward the viewpoint 530 doesnot intersect any other objects (e.g., 550 in FIG. 5). This extrusiontest can be performed, for example, by projecting any point or locus ofpoints on the object 520 in a direction towards the viewpoint 530. Ifthis projection yields no intersections with other objects 550, then theline of sight 540 can be considered to be cleared, and the minimummagnitude of the occlusion reduction displacements has been achieved.This criterion provides a means of testing whether a given displacementoperation or other occlusion reduction method has resulted in theelimination or reduction of occlusion. The extrusion of all objectpoints in this manner defines a volume which must be cleared ofobstructions for the complete elimination or reduction of occlusion.Advantageously, such an extrusion coupled with the orthogonaldisplacement as described above from U.S. Pat. No. 6,798,412 defines aminimum displacement from the line of sight 540 and hence an optimalocclusion reduction.

According to another embodiment, a method for the subdivision ofpolygons to improve displacement quality is provided. For reference,FIG. 8 is a diagram illustrating a distortion function 230 or lens 410.In operation, the lens 410 may be adjusted with the GUI 400 of FIG. 4.FIG. 9 is a diagram illustrating an original image or representation inthe form of a mesh 900 composed of polygons (e.g., triangles) 910. And,FIG. 10 is a detail view of a portion of the mesh 900 of FIG. 9. In FIG.8, the lens 410 is defined by a distortion function 230 that is aGaussian function. The mesh 900 of FIG. 9 is fitted to the distortionfunction 230 or lens 410 of FIG. 8 in that the mesh 900 is aligned tothe Hessian of the Gaussian function (i.e., the polygons near the centreof the mesh 900 are smaller in size than those near the outer edges ofthe mesh). Of course, the mesh 900 may have polygons 910 that are notpre-fitted to the lens 410. In any event, with such a mesh 900 defined,the application of a lens 410 to an original image may be simplified asin general only the vertices 920 of each polygon 910 need be displaced.Points lying between the vertices 920 may then be interpolated. Themethod described here with respect to FIGS. 8-10 is one approach ofgenerating a random looking mesh in the hope that it will closelyapproximate a lens. What will be described next is an improvedmethodical approach to meshing a polygon.

When dealing with 3D polygonal (e.g., triangle 910 shown in 2D in FIG.9) data, displacing existing vertices 920 is often not enough to producea good quality lensed scene. For example, a problem arises whenindividual triangles 910 are large in relation to the lens 230, 410. Inthese cases it is possible for the triangles 910 to overlap the lens410, but have no vertices 920 in the lens 410, under which circumstancenone of the vertices 920 would be displaced. This can result in anon-ideal situation where a triangle 910 is not displaced even though itintersects the lens 410. As another example, it is possible for one ormultiple vertices 920 to lie within the lens 410, under whichcircumstance those vertices 920 would be displaced, but the connectingedges 930 would remain straight, not curved according to the geometryspecified by the lens 410. The solution to these problems in thisembodiment is to subdivide triangles 910 that intersect the lens 410 insuch a way that the displaced triangles will adequately approximate thedistortion specified by the lens 410. This is accomplished by insertingextra vertices 920 and edges 930 into the triangle geometry 900. In thecase of a circular lens 410 with a circular focal region 420, forexample, a circle of edges 930 around the bounds or perimeter (e.g., 411or 412) of the lens 410, one around the focal bounds or perimeter (e.g.,421) of the lens 410, and possibly one or more at intermediate points(e.g., 430) in between the focal region 420 and the bounds 411, 412 isinserted. According to another embodiment, additional edges 930 andvertices 920 may be inserted radially from the center of the lens 410,like bicycle spokes, to improve the appearance of the lens 410.

Note that the notion of a “mesh”, while appropriate for 2D applications,is not entirely appropriate for 3D applications. For 3D applications,the expression a “collection of polygons” is more appropriate as ingeneral 3D data is considered to be a collection of isolated triangles(polygons). In the method described above, what is accomplished is themeshing of a polygon 910, or a subdividing of a polygon into manypolygons. Thus, for 3D applications, FIGS. 9 and 10 may be described asillustrating a “collection of polygons” 900 rather than a mesh composedof polygons. For example, in the case of a CAD drawing with multipleparts, there could be a separate mesh or collection of polygonsassociated with each part.

Another difference between 2D and 3D applications is that in 3Dapplications, data vertices 920 can be located anywhere in the 3D space.This affects the manner in which a detail-in-context presentation for anoriginal 3D image is generated. In particular, with respect to lensdefinition, in 2D, the lens (e.g., 230 in FIG. 2) is defined as existingin the plane 210 of the original image or data. However, in 3D, there isno inherent data plane 210. Therefore, an arbitrary plane is chosen onwhich the lens 410 may be defined. The arbitrary plane can be chosen tobe orthogonal to the line of sight (e.g., 231 in FIG. 2). The lens canbe defined on the arbitrary plane and then projected onto a view plane(e.g., 201 in FIG. 2) or screen to achieve a desired size ormagnification.

Now, to subdivide the triangles or polygons 910 to adequatelyapproximate the distortion specified by the lens 410, a first step isproject the perimeter of the lens 411, 412 and/or focal region 421 ontothe arbitrary plane. This projection may be a perspective projection oran orthonormal projection. After the subdivision of polygons 910, theresulting collection of polygons are displaced onto the lens 410 andperspectively projected onto a view plane in a viewpoint aligneddirection.

Note that occlusion reduction can also be performed with an orthonormalcamera projection. In an orthonormal projection, first, an arbitraryperspective projection is used with a standard displacement function (asdescribed above), second, the point to be displaced is translated ontothe lens surface, and third, the point is perspectively projected ontothe desired plane. The difference between this new point and theoriginal point is what is used for the displacement in an orthonormalprojection.

According to another embodiment, a method for providing a lens-dependentlevel of detail in a presentation is provided. Now, 3D models cansometimes be very complex, taxing the processor 320 and memory 330subsystems of a data processing system 300. Reducing model complexitycan help deal with this problem. Coupling level of detail with lensposition can be used to keep polygon count in a mesh 900 low, whilestill providing high polygon counts where they are needed. The low levelpolygon count models can be arrived at in several ways. First, a usercan explicitly specify a simple geometry version of a complex assembly.For example, the rendering software 331 may be instructed to replace acomplex engine assembly in a representation of an automobile with asimple cylinder assembly. Second, the rendering software 331 can useautomated model simplification algorithms to arrive at simpler models,provided that these algorithms themselves are not excessivelycomputationally expensive.

According to another embodiment, 3D magnification lenses and a methodfor occlusion reduction with magnification are provided. In thisembodiment, detail-in-context lens magnification, as described in U.S.Pat. Nos. 6,768,497 and 6,798,412 and U.S. patent application Ser. Nos.10/021,313, 10/137,648, and 10/166,736, which are incorporated herein byreference, is extended to magnification of 3D objects. Algorithmically,there are several methods of providing this. One method is to project 3Ddata vertices onto a plane perpendicular to the line of sight, apply a2D lens to the vertices (e.g., 920) in the plane, and then “un-project”the vertices back into 3D. An occlusion reduction operation for themagnified object can then be applied after the magnification step (i.e.,the application of the 2D lens). The un-project step may be performed intwo ways. The first method is to translate the lensed point along a linespecified by the viewpoint and the lensed point, a distance equal to thedistance of the original projection. The direction of translation isopposite to the original projection. The second method is the same asthe first, except the distance of the translation is calculated suchthat the point will be co-planar with the original data vertex point,with the plane defined as being perpendicular to the line of sight.

According to another embodiment, a method for selective and automaticocclusion reduction based on object recognition or object attributes isprovided. In many cases it is desirable to preserve the location ofspecific occluding objects, to prevent the separation of related orgrouped objects, or to limit the allowed displacement of specificobjects. According to this embodiment, pattern recognition or objectrecognition methods are used to automatically detect specific objects(e.g., 550 in FIG. 5) and apply known constraints to their alloweddisplacements. For example, an object of interest may be recognized byquerying a database or table of object features of a given assembly witha query containing identifying parameter values of theobject-of-interest. Alternately, raster pattern matching algorithms maybe applied to compare a digital photograph of the part of interest withthe actual rendered objects of the assembly to identify a matching part.According to another embodiment, maximum displacements and relatedattributes are stored with the objects and retrieved during theocclusion reduction operations to constrain object displacements.

The above described method (i.e., with respect to polygon subdivision)may be summarized with the aid of a flowchart. FIG. 11 is a flow chartillustrating operations 1100 of software modules 331 within the memory330 of a data processing system 300 for generating a presentation of aregion-of-interest in an original image for display on a display screen340, the original image being a collection of polygons 900 havingpolygons 910 defined by three or more shared edges 930 joined at vertexpoints 920, in accordance with an embodiment.

At step 1101, the operations 1100 start.

At step 1102, a lens 230, 410 is established for the region-of-interest,the lens 230, 410 having a magnified focal region 233, 420 for theregion-of-interest at least partially surrounded by a shoulder region234, 430 across which the magnification decreases, the focal andshoulder regions having respective perimeters 421, 412.

At step 1103, polygons 910 of the collection of polygons 900 proximateto at least one of the perimeters 421, 412, as projected with thepolygons 910 onto a base plane 210, are subdivided by inserting one ormore additional vertex points 920 and additional edges 930 into thepolygons 910 to be subdivided.

At step 1104, the lens 230, 410 is applied to the original image toproduce the presentation by displacing the vertex points 920 onto thelens 230, 410 and perspectively projecting the displacing onto a viewplane 201 in a direction 231 aligned with a viewpoint 240 for theregion-of-interest.

At step 1105, the operations 1100 end.

Preferably, the method further includes positioning the one or moreadditional vertex points and additional edges to align with the at leastone of the perimeters 421, 411, 412. Preferably, the focal region 420has a size and a shape and the method further includes receiving one ormore signals to adjust at least one of the size, shape, andmagnification of the focal region 420. Preferably, the method furtherincludes displaying the presentation on the display screen 340.Preferably, the lens is a surface. Preferably, the method furtherincludes receiving the one or more signals through a graphical userinterface (“GUI”) 400 displayed over the lens 410. Preferably, the GUI400 has means for adjusting at least one of the size, shape, andmagnification of the focal region 420. Preferably, at least some of themeans are icons. Preferably, the means for adjusting the size and shapeis at least one handle icon 481, 482 positioned on the perimeter 421 ofthe focal region 420. Preferably, the means for adjusting themagnification is a slide bar icon 440, 441. Preferably, the methodfurther includes receiving the one or more signals from a pointingdevice 310 manipulated by a user. Preferably, the pointing device 310 isat least one of a mouse, a trackball, and a keyboard. Preferably, theshoulder region 430 has a size and a shape and further comprisingreceiving one or more signals through a GUI 400 displayed over the lens410 to adjust at least one of the size and shape of the shoulder region430, wherein the GUI 400 has one or more handle icons 491 positioned onthe perimeter 411, 412 of the shoulder region 430 for adjusting at leastone of the size and the shape of the shoulder region 430. Preferably,the method further includes selecting the base plane 210. Preferably,the polygons 910 are orthonormally projected onto the base plane 210.Preferably, the polygons 910 are perspectively projected onto the baseplane 210. Preferably, the original image is a three-dimensionaloriginal image. Preferably, the method further includes positioning theone or more additional vertex points 920 and additional edges 930 toalign with radii of the lens 410.

While this discussion involved a method, a person of ordinary skill inthe art will understand that the apparatus discussed above withreference to a data processing system 300, may be programmed to enablethe practice of the method. Moreover, an article of manufacture for usewith a data processing system 300, such as a pre-recorded storage deviceor other similar computer readable medium including program instructionsrecorded thereon, may direct the data processing system 300 tofacilitate the practice of the method. It is understood that suchapparatus and articles of manufacture also come within the scope.

In particular, the sequences of instructions which when executed causethe method described herein to be performed by the data processingsystem 300 of FIG. 3 can be contained in a data carrier productaccording to one embodiment of the invention. This data carrier productcan be loaded into and run by the data processing system 300 of FIG. 3.In addition, the sequences of instructions which when executed cause themethod described herein to be performed by the data processing system300 of FIG. 3 can be contained in a computer software product accordingto one embodiment. This computer software product can be loaded into andrun by the data processing system 300 of FIG. 3. Moreover, the sequencesof instructions which when executed cause the method described herein tobe performed by the data processing system 300 of FIG. 3 can becontained in an integrated circuit product including a coprocessor ormemory according to one embodiment of the invention. This integratedcircuit product can be installed in the data processing system 300 ofFIG. 3.

The embodiments described above are intended to be exemplary only. Thescope of the invention is therefore intended to be limited solely by thescope of the appended claims.

1. One or more computer-readable media comprising instructions storedthereon, that responsive to being executed by a data processing system,cause the data processing system to perform operations comprising:displacing objects that occlude an object-of-interest in an image, awayfrom a line of sight between a viewpoint and the object-of-interest,wherein the objects are displaced away from the line of sight based on atransform function and minimum displacements determined from a volumedefined by extrusion of surface points included on theobject-of-interest towards the viewpoint; and generating a presentation,from the viewpoint's perspective, that includes the objects displacedaway from the line of sight so that the object of interest is notoccluded and additional objects included in the image remain visible. 2.The one or more computer-readable media of claim 1, wherein the volumecomprises an exclusion volume that is cleared of the objects.
 3. The oneor more computer-readable media of claim 1, wherein the image comprisesa medical image.
 4. The one or more computer-readable media of claim 3,wherein the medical image represents at least a portion of a human body.5. The one or more computer-readable media of claim 1, wherein theinstructions further comprise instructions that, responsive to beingexecuted by the computing system, cause the computing system to magnifythe object of interest, in comparison to the object of interest's sizein the image, prior to extrusion of the surface points.
 6. The one ormore computer-readable media of claim 5, wherein a magnified region,that includes the object of interest, is at least partially surroundedby a shoulder region.
 7. The one or more computer-readable media ofclaim 1, wherein the instructions further comprise instructions that,responsive to being executed by the computing system, cause thecomputing system to accept an input that specifies the viewpoint.
 8. Theone or more computer-readable media of claim 1, wherein the objects aredisplaced perpendicular to the line of sight.
 9. The one or morecomputer-readable media of claim 1, wherein the surface points comprisevertices of a polygon.
 10. One or more computer-readable mediacomprising instruction stored thereon, that responsive to being executedby a data processing system, causes the data processing system toperform operations comprising: displace one or more objects away from aline of sight between an object-of-interest and a viewpoint responsiveto selection of the viewpoint to view the object-of-interest based on atransform function and minimum displacements determined throughextrusion of surface points on the object of interest towards theviewpoint, wherein the one or more objects would at least partiallyocclude the object of interest from the viewpoint's perspective, but fordisplacement of the one or more objects; and generate a presentation,from the viewpoint's perspective for presentation on a display deviceassociated with the computing system, in which the object of interest isnot occluded by the one or more objects.
 11. The one or morecomputer-readable media of claim 10, wherein selection of the viewpointis accomplished by clicking on an image.
 12. The one or morecomputer-readable media of claim 11, wherein the image comprises a scanof at least a portion of a human body.
 13. The one or morecomputer-readable media of claim 11, wherein the image comprises amagnetic resonance image (MRI) of at least a portion of a human body.14. The one or more computer-readable media of claim 10, wherein theinstructions further comprise instructions that, responsive to beingexecuted by the computing system, cause the computing system to: displayan image on the display device associated with the computing system; andaccept an input that selects the viewpoint.
 15. The one or morecomputer-readable media of claim 10, wherein the computing system isconfigured to receive a scan from a medical device.
 16. The one or morecomputer-readable media of claim 10, wherein the instructions furthercomprise instructions that, responsive to being executed by thecomputing system, cause the computing system to magnify the object ofinterest prior to extrusion of the surface points.
 17. The one or morecomputer-readable media of claim 10, wherein the object of interestcomprises a portion of a human body.
 18. The one or morecomputer-readable media of claim 10, wherein the object of interestcomprises a portion of a human brain.
 19. A method comprising:displacing a representation of a body part in a scan that originallyobstructed a representation of a body part of interest in the scan, awayfrom a line of site between a viewpoint and the representation of thebody part of interest, wherein the representation of the body part isdisplaced away from the line of sight based on a transform function anda minimum displacement determined from a volume defined by extrudingsurface points included on the representation of the body part ofinterest towards the viewpoint; and generating a presentation from theviewpoint's perspective that includes the representation of the bodypart displaced away from the line of sight so the representation of thebody part of interest is not occluded in the presentation andrepresentations of additional body parts represented in the scan arevisible in the presentation.
 20. The method of claim 19, wherein thescan comprises a magnetic resonance image (MRI) of at least a portion ofa human body.
 21. The method of claim 19, wherein the representation ofthe body part of interest comprises a portion of a human brain.
 22. Themethod of claim 21, wherein the scan comprises one or more x-rays of ahuman body.
 23. The method of claim 19, further comprising selecting theviewpoint by receiving an input that clicked on the scan.